1. Field of the Invention
The present invention relates to an image forming machine such that both sides printing can be easily conducted although structure of a sheet supplying device and a sheet discharging device is simple.
2. Description of the Related Art
A stencil printing machine will be explained as an example of the image forming machine.
FIG. 5 illustrates an example of a conventional stencil printing machine. A cylindrical printing drum 100 is rotatable around an axis 100a thereof. An ink permeable area is formed in a part of a peripheral wall of the printing drum 100. Inside the printing drum 100, an ink supplying means 100b is situated for supplying ink to an inner circumferential surface of the peripheral wall. A clamping device 101 is attached to an outer circumferential surface of the peripheral wall of the printing drum 100 for holding a leading end of a stencil sheet. The stencil sheet held by the clamping device 101 at the leading end thereof is wound around the outer circumferential surface of the printing drum 100.
Beneath the printing drum 100, a cylindrical opposing drum 102 is rotatably situated. The opposing drum 102 is rigid and not deformed during printing. The diameter of the opposing drum 102 is approximately identical to that of the printing drum 100. An axis of the opposing drum 102 is parallel to the axis of the printing drum 100. The opposing drum 102 is arranged so as to practically contact the printing drum 100. A holding claw 103 is attached to an outer circumferential surface of the opposing drum 102. A recess 104 is formed in the outer circumferential surface of the opposing drum 102 for avoiding interference with the clamping device 101 of the printing drum 100.
The printing drum 100 and the opposing drum 102 are rotated in synchronization with each other and in directions opposite to each other. The drums convey a printing sheet while holding it therebetween, and conduct printing on it.
Above a sheet supplying table 105, a sheet supplying roller 106 is situated. Between the sheet supplying roller 106 and the printing drum 100, a timing roller 107 is situated. On a discharging side of the printing drum 100, there are disposed a discharging claw, 108 for peeling the printing sheet from the opposing drum 102, a pinch roller 109, and a discharging roller 110 for conveying the printing sheet. The printing sheet as printed is fed out by the discharging roller 110 onto a sheet discharging table 113.
According to the conventional stencil printing machine as explained above, the printing sheet is taken by the sheet supplying roller 106 and the timing roller 107, held by the holding claw 103 of the opposing drum 102 at the leading end thereof, and then conveyed along the outer circumferential surface of the opposing drum 102 upon rotation of the opposing drum 102. And, the printing sheet is printed while being held between the printing drum 100 and the opposing drum 102. The printing sheet as printed is released from the holding claw 103 and sent out by the discharging roller 110 onto the discharging table 113.
The conventional stencil printing machine includes a driving mechanism for vertically moving the sheet supplying table 105. Further, the printing machine includes a detecting means for detecting height of the printing sheets stacked on the sheet supplying table 105. This constitution allows the printing sheet on the sheet supplying table 105 to be situated to an optimum position for being sent out by the sheet supplying roller 106.
Further, the printing machine includes a driving mechanism for vertically moving the sheet discharging table 113. Further, the printing machine includes a detecting means for detecting height of the printing sheets stacked on the sheet discharging table 113. That constitution allows the discharging table 113 to be situated to a position such that the printing sheet as printed is discharged onto the sheet discharging table 113 without crimping and jamming so that the discharged sheets are orderly stacked.
However, according to the conventional stencil printing machine as explained above, the sheet supplying table 105 and the sheet discharging table 113 are situated to a front and a rear side of the printing drum 100 and the opposing drum 102, respectively, in a direction of conveying the printing sheet. Therefore, the driving mechanism and the detecting means are required to be provided to each of the sheet supplying table 105 and the sheet discharging table 113. Further, a control means is necessary for each of the sheet supplying table 105 and the sheet discharging table 113 for controlling movement of them. Further, enough space must be ensured for each of the sheet supplying table 105 and the sheet discharging table 113 for allowing them to move vertically. Additionally, the sheet supplying table 105 includes an adjustable sheet supplying fence 115 for guiding an outer edge of the printing sheet, and the sheet discharging table 113 includes an adjustable sheet discharging fence 116 for guiding the outer edge of the printing sheet. And, the sheet supplying fence 115 and the sheet discharging fence 116 must be adjusted according to a size of the printing sheet, respectively.
Further more, in the case where both sides of the printing sheet is needed to be printed, after the printing sheets are printed on one surface thereof, the printing sheets stacked on the sheet discharging table 113 are taken therefrom to be replaced on the sheet supplying table 105 upside-down. However, such operation that the printing sheets are moved from one table to another is troublesome. And, during the operation, the stacked sheets may shift to be rubbed with each other, thereby being deteriorated in printed image quality.
An object of the present invention is to provide an image forming machine of simple constitution that is capable of conducting optimum sheet supplying/discharging operations by moving the sheet supplying/discharging tables interlocked with each other and facilitating handling of the printing sheets during both sides printing.